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Tools for writing mobile software
Matt Nicholson explains how Microsoft?s range of mobile tools and platforms support a number of different application architectures.
Author: Matt Nicholson
Last updated: Mar 2004
Developing applications for mobile devices, or extending existing applications
to take advantage of mobile devices, can appear daunting. The market is
moving so fast, and there are so many different standards, that deriving
a viable long-term strategy seems impossible. The ASP.NET approach The Managed approach Native code applications Making your choice Part of Microsoft’s Windows Embedded Family, Windows CE is a 32-bit
operating system with real-time processing support, including timer accuracy
of 1 millisecond, support for nested interrupts and 256 levels of priority.
The operating system runs on a wide range of processors, including ARM,
MIPS and SH-based architectures, and is modular in design, which means
you can choose just the components you need for a particular device. Pocket PC 2003 Pocket PC 2002 Phone Edition added data and voice applications for triple-band
wireless connectivity through GSM and GPRS. Smartphone 2003
Microsoft has approached this problem
by extending its existing tools out into the mobile world, and by developing
an operating system for mobile devices that offers an API consistent with
its desktop counterparts. This at least ensures developers can work in
a familiar environment when they enter this brave new world. Microsoft’s
mobile platforms come under the generic Windows Mobile brand, with the
current iteration being Windows Mobile 2003.
Mobile devices come in different shapes
and sizes. On the one hand are Personal Digital Assistants (PDAs) that
have a relatively large screen and respectable processing and storage
capabilities. Microsoft’s principal platform here is Pocket PC which
is based on the Windows CE operating system. The latest version is Pocket
PC 2003 which, like all Windows Mobile 2003 platforms, is based on Windows
CE 4.2 and processors compatible with Intel’s ARM instruction set.
Competing platforms include Palm and Handspring.
On the other hand are mobile phones
which offer much less in the way of local storage and processing power
but provide data connectivity through GSM, GPRS or 3GSM. Many of these
can browse the Internet through their support of WML (WAP Markup Language)
although these are being replaced by devices capable of displaying HTML.
More recently we have seen hybrid
devices emerging which combine wireless connectivity, whether through
wide-area technologies such as GPRS or through more local-area technologies
such as Wi-Fi, with more powerful processing and storage capabilities.
Microsoft has moved into this space with two platforms, again based on
Windows CE. As its name suggests, Pocket PC Phone Edition adds connectivity
to the Pocket PC platform. The other is Smartphone which offers a smaller
platform designed for a new generation of mobile handset. Current versions
are Pocket PC 2003 and Smartphone 2003. These compete with a wide range
of platforms offering Web browsing facilities or supporting J2ME (Java
2 Micro Edition).
One of the strengths of Microsoft’s
strategy in this market is the wide range of options it allows you to
take when designing applications for such devices, which we will now examine
in more detail.
One option is to extend the Web application model where the bulk of the
processing is carried out on back-end servers which deliver the application
interface to mobile devices as HTML or WML pages. The advantage of such
an approach is the wide range of devices that can be accommodated. The
disadvantage is that the application can only work when the mobile device
is connected to the server.
At the heart of Microsoft’s
platform for delivering Web applications is the .NET Framework, and at
the core of the .NET Framework is the Common Language Runtime (CLR). Code
written for the .NET Framework is not compiled directly to binary code
but instead to Microsoft Intermediate Language (MSIL) which is in turn
compiled to binary code by the high-performance compiler built in to the
CLR.
It is the CLR that activates objects,
performs security checks, verifies type safety and allocates memory. It
also manages memory through an extremely efficient garbage collector.
As a result, code written for the .NET Framework (usually referred to
as ‘managed’ code) tends to be more reliable and more secure
than code that is compiled directly to machine code, and so does not take
advantage of the services offered by the CLR.
The .NET Framework comes with one
of the largest class libraries ever built, containing over 5,000 classes
divided into a set of over 90 namespaces. One of these is the System.Web
namespace which replaces Active Server Page (ASP) technology with a coherent
set of classes for generating dynamic HTML-based content and XML Web Services
which is called ASP.NET. You can write ASP.NET applications using any
of the languages supported by Visual Studio .NET, including Visual Basic
.NET, C# and J#, and these applications can access corporate databases
and legacy systems through ADO.NET, or any of the other integration libraries
that come with the .NET Framework. They can also make use of the COM+
Services built into Windows 2000 and Windows Server 2003.
Microsoft has extended ASP.NET to
cater for mobile devices through the provision of ASP.NET Mobile Controls.
These are server-side controls that emit HTML or WML in a form suitable
for mobile devices, which is then tailored to the needs of specific devices
by installable Device Adapters. The technology has been tested with more
than 200 third-party devices and supports WAP, iMode, Palm, Symbian and
Handspring browsers, as well as Pocket Internet Explorer which is included
with Pocket PC and Smartphone.
You work with ASP.NET Mobile Controls
within the Visual Studio .NET environment in much the same way as you
would conventional ASP.NET controls, although there are some differences.
For example, you can place multiple Mobile Web Forms on a single page,
each containing different Mobile Controls. If the target is a WAP device
then all the forms are downloaded in one go, and the user can navigate
between them without further traffic between the device and the server.
If the device uses a Web browser then each form is downloaded as a separate
HTML document.
This technology is included in Visual
Studio .NET 2003. The .NET Framework itself is built in to Windows Server
2003, or is available as a free download for use with earlier versions
of Windows.
The ASP.NET approach is ideal if you
need to target a wide range of devices, as for example in a ticket-booking
service that is available to the general public. However the application
can only function when the client device is connected to the server. If
the user wanders out of range, or is unable to attach to the Internet,
then the application ceases to function. This architecture is not suited
to applications where the user wants to collect data on the client for
later synchronisation when a connection can be established, or for stand-alone
applications that rely on the processing and data handling capabilities
of the device itself. Such applications require a different approach.
Although the Pocket PC and the Smartphone function as very viable ASP.NET
client, such an approach does not make best use of the considerable computing
power available on the device itself. These days a Pocket PC can contain
a 400MHz 32-bit processor linked to 128Mb of memory, or up to 1Gb through
CompactFlash cards, which is equivalent in power to a typical desktop
PC only a few years ago.
To take advantage of this power, Microsoft
has developed the .NET Compact Framework. This is an implementation of
the .NET Framework targeted at devices running Windows CE .NET. It is
supported by Pocket PC 2002 and 2003, and by Smartphone 2003, but not
by older Smartphone 2002 devices.
The .NET Compact Framework uses the
same programming model as its big brother, and includes a compact version
of the CLR. However it is optimised for devices with smaller resources
and saves memory by providing a subset of the .NET Framework class library.
For full details, see our article elsewhere (click here).
Visual Studio .NET 2003 includes the
.NET Compact Framework together with the tools you need to write .NET
applications for mobile devices in either Visual Basic .NET or C#. Windows
CE .NET includes the .NET Compact Framework as one of its component parts
which means hardware manufacturers can use the Windows CE .NET Platform
Builder to install .NET Compact Framework onto their devices. Alternatively,
the .NET Compact Framework can be downloaded from a desktop PC and installed
onto a Windows Mobile device using ActiveSync, either as part of an application
installation or on its own.
The .NET Compact Framework offers
many options for persisting data on the device, and for synchronising
locally-stored data with server-side data. Synchronisation can be achieved
through ActiveSync, or the mobile application can interact with a Web
Service exposed by the server. All these options are supported by the
ADO.NET classes provided by the .NET Compact Framework.
However the most powerful option for
data storage is that provided by SQL Server CE. This relational database
management system delivers a remarkably large subset of the facilities
provided by SQL Server itself, including a fully compatible set of data
types, all in a footprint of under 2Mb. Features include enforced referential
integrity with cascading deletes and updates, multi-column indexing with
up to 32 indexes per table, scrollable and forward only cursors, and 128-bit
data file encryption.
SQL Server CE offers two techniques
for synchronising with SQL Server itself, both achieved using HTTP. On
the one hand, Remote Data Access (RDA) provides a rather crude mechanism
for pushing or pulling data between SQL Server CE and either SQL Server
7.0 or SQL Server 2000. Alternatively, the SQL Server CE Replication object
allows you to perform a full merge replication with SQL Server 2000. Communication
is achieved through an ISAPI filter called the SQL Server CE Agent which
must be installed into Internet Information Server (IIS).
SQL Server CE has been around rather
longer than the .NET Compact Framework. However version 2.0 has been specifically
designed to work with managed code. In particular, the new Data Access
Architecture provides .NET classes for managing replication and Remote
Data Access. Interaction with the data itself is achieved through ADO.NET.
The alternative to a managed application, running under .NET Compact Framework,
is a native code or ‘unmanaged’ application running directly
against the Windows CE API. This is the only type of application that
will run on older Smartphone 2002 devices, and there are still plenty
of instances on the Pocket PC and Smartphone 2003 platforms where native
code makes more sense.
Developing native code applications
for Windows CE devices such as the Pocket PC or Smartphone is achieved
using either the eMbedded Visual Tools 3.0 suite or eMbedded Visual C++
4.0.
The eMbedded Visual Tools 3.0 suite
includes two stand-alone development environments, both similar to the
Visual Studio 6.0 environment. The first is eMbedded Visual C++ (eVC)
3.0 which includes versions of both MFC (Microsoft Foundation Classes)
and ATL (ActiveX Template Libraries) and allows you to build high-speed
applications, components or device drivers that run as native code on
the device.
The second is eMbedded Visual Basic
(eVB) 3.0 which is more like VBScript than Visual Basic itself. This is
an interpreted language, requiring installation of a runtime on the device
itself, and does not include support for class modules. The eVB environment
is being phased out and it is now only supported for Pocket PC 2002 devices.
Both eVC and eVB support ActiveX Data Objects for Windows CE (ADOCE),
which gives you access to SQL Server CE (see above).
These development environments are
supported by the Software Development Kit (SDK) appropriate to the target
device. The suite comes with SDKs for all Windows Mobile platforms, including
the Pocket PC 2003 SDK and the Smartphone 2003 SDK. While the Pocket PC
2002 SDK supports development in both eVB and eVC++, all other Windows
Mobile SDKs support only eVC++.
The SDKs include a range of useful
tools such as the Remote Registry Editor, Remote Heap Walker and Remote
Process Viewer which help you debug your application through the device’s
USB or serial port as it runs on the device itself. Both also include
emulators for testing your application locally. These emulators actually
run Windows CE binaries within a virtual machine on your desktop, making
them far more accurate than those of earlier SDKs.
The SDKs also give you access to the
Pocket Outlook Object Model (POOM), which allows you to hook your applications
into Pocket Outlook. Using POOM you could, for example, extend the Pocket
Outlook Tools menu to display an order history for the current contact,
based on data extracted from SQL Server CE.
The eMbedded Visual Tools 3.0 suite
is targeted at the Windows CE 3.0 operating system, rather than Windows
CE .NET. Microsoft has released eVC++ 4.0 for developers wishing to work
with Windows CE .NET. There will not be a new version of eVB as Visual
Basic programmers will be able to use Visual Basic .NET itself to write
managed code for the .NET Compact Framework.
New features of eVC++ 4.0 include
support for catch/throw exception handling as well as Win32 structured
exception handling, Standard Template Library (STL) support, and access
to Run Time Type Information (RTTI) which allows you to determine object
type at runtime. There is also full support for the new debugging features
enabled by Windows CE .NET, and a new call trace tool in the Remote Call
Profiler.
Note that eVC++ 3.0 is still needed
if you wish to write native code for the Pocket PC 2002 and Smartphone
2002 platforms. However eVC++ 4.0 can be installed on the same machine
as eVC++ 3.0 without causing problems.
Microsoft is well known for the quality of its development tools, and
this continues when it comes to developing for mobile devices. The key
is familiarity. Even if you are using the eMbedded Visual Tools suite
to develop native code applications for the Pocket PC or Smartphone, you
will still find yourself in a familiar environment, working with familiar
languages, and programming against a familiar API.
If your target is the .NET Compact
Framework, or you’re building an ASP.NET application that targets
mobile devices, then you can use the same tools as you would building
a standard desktop or server application, and be able to take full advantage
of all the facilities provided by Visual Studio .NET. You will of course
have to familiarise yourself with the .NET Compact Framework, or the ASP.NET
Mobile Controls, but you won’t have to learn a completely different
operating system, or get to grips with a completely new toolset.
As a result, mobile software development
need no longer be seen as a specialist area, requiring specialist tools
and specialist skills. Instead developers can integrate mobile devices
into their applications using the same tools and technologies as they
use for their desktop clients, and take full advantage of the facilities
offered by the .NET platform.
The Windows CE Family
In the case of the Pocket PC and Smartphone,
Microsoft has defined the platform and created the supporting SDKs for
you. However you can use the Windows CE Platform Builder to configure
the operating system and create the SDK for your own custom hardware.
Once you have done this you can distribute the SDK to developers so they
can write applications for your device. Platform Builder 3.0 supports
Windows CE 3.0 and comes with eMbedded Visual Tools 3.0. Platform Builder
4.0 supports Windows CE .NET.
Windows CE 3.0 includes support for
COM and DCOM, Microsoft Message Queue, ActiveX Data Objects (ADOCE), XML
and Microsoft Foundation Classes (MFC). It also includes the runtimes
for eVB 3.0 and eVC++ 3.0. The Windows CE 3.0 Add-On Pack adds support
for DirectX and Windows Media.
Windows CE .NET 4.1 and 4.2 include
the .NET Compact Framework, but will only run on processors based on the
ARM architecture. They also support fibers (as introduced with Windows
XP), and have a number of new features that allow applications to make
better use of memory. Windows CE .NET adds supports catch/throw exception
handling, and the COM subsystem has been rewritten to improve stability.
Other additions include support for
Bluetooth and 802.11, Secure Digital (SD) and MultiMediaCard (MMC), Object
Exchange (OBEX) protocol for efficient exchange of data, Universal Plug
and Play (UPnP), IEEE 1394, LDAP, Active Template Library (ATL) and Windows
Messenger. Windows CE .NET 4.2 adds zero-configuration Wi-Fi support (similar
to that found in Windows XP) and an accessible certificate store that
enables PKI applications such as 802.1x.
Platform specifications
Pocket PC 2003 is a configuration of Windows CE 4.2 with extensions specifically
targeted at pocket-sized devices where input is through a stylus, rather
than a keyboard. The original Pocket PC platform was introduced in 2000
and has since been superseded by Pocket PC 2002 and 2003. Requirements
include:
External storage through SD (Secure Digital), MMC (MultiMediaCard) or
CompactFlash.
Microsoft’s Smartphone 2003 platform is also based on Windows CE
4.2 but is aimed at devices modelled on the mobile phone. The original
Smartphone 2002 specification did not support .NET Compact Framework,
however this is supported by Smartphone 2003. Requirements include:
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